Plant growth regulators

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Plant Hormones and Plant Growth Regulators

Another factor in plant growth is the influence of plant hormones.  Hormones are chemicals produced by plants that regulate the growth processes.

Plant growth regulators are chemicals applied by a horticulturist to regulate plant growth.  In plant propagation, cuttings are dipped in a rooting hormone to stimulate root development.  In greenhouse production, many potted flowering plants may be treated with plant growth regulators to keep them short.  Seedless grapes are treated with plant growth regulators to increase the size of the fruit.  In special situations, turf may be treated to slow growth and mitigate the need for mowing.  

Plant Hormones

Different hormones affect different plant processes.  Understanding how hormones work allows horticulturists to manipulate plants for specific purposes. 

• Auxins produced in the terminal buds suppress the growth of side buds and stimulate root growth.  They also affect cell elongation (tropism), apical dominance, and fruit drop or retention.

• Gibberellins affect:


• The rate of cell division
• Flowering
• Increase in size of leaves and fruits
• Seed and bud dormancy
• Induction of growth at lower temperatures (used to green up lawns 2 to 3 weeks earlier)


• Cytokinins promote cell division, and influence cell differentiation and aging of leaves.


• Abscisic acid is considered the “stress” hormone.  It inhibits the effects of other hormones to reduce growth during times of plant stress.